1. Field of the Invention
The present invention relates to preparation of an N-[1-(thienyl)alkyl]amine derivative, particularly preparation of an N-[1-(thienyl)alkyl]amine derivative through an amidoalkylation reaction in a single stage.
2. Description of the Related Art
An N-[1-(thienyl)alkyl]amine derivative, for example, an N-[1-(thienyl)ethyl]amine derivative has herbicidal activity and is extraordinarily effective against lowland annual weeds such as Echinochloa oryzicola Vasing., Cyperus difformis L., Monochoria vaginalis Presl, Lindernia procumbens Philcox, Rotala indica Koehne and Elatine triandra Schk. and against upland weeds such as Echinochloa frumentacea Link, Digitaria adscendens Henr., Abutilon avicennae Gaertn., Amaranthus viridis L. and Bidens biternata Merr. et Sherff (cf., for example, Japanese Patent Kokai Publication No. 2987/1988).
To prepare an amine derivative of the formula: ##STR5## wherein R.sub.1 is an organic group, R.sub.2 is a hydrogen atom or a lower alkyl group, and R.sub.3 is a hydrogen atom or an organic group, which includes the above amine derivative through an amidoalkylation reaction, conventionally the following stepwise process is employed: ##STR6##
The reason why such stepwise process has been conventionally used is that it does not yield a by-product if the intermediate prepared in the step (1) is isolated and reacted with R.sub.1 H. When R.sub.2 is a hydrogen atom, the stepwise process achieves a high conversion since the intermediate 1 can be isolated. When R.sub.2 is not a hydrogen atom, the intermediate 2 other than the intermediate 1 is obtained. In this case, the starting amide is also produced as shown in the step (2'), and therefore the conversion does not exceed 50% even if the reaction of the step (2') proceeds quantitatively.
As a method of preparing said amine derivative, is known the reaction of ##STR7## wherein R.sub.1, R.sub.2 and R.sub.3 are the same as defined above, and B.sub.1 is a hydroxy group, an alkoxy group or a halogen atom. However, this method needs a separate route to prepare the reactants and is a multistep reaction.